1. Field of the Invention
The present invention relates to an optical disk and an optical-disk information reproducing method of reproducing recorded information from the optical disk.
2. Description of the Related Art
Conventional optical disks, such as compact disks (CDs) or video disks (VDs), have pit information recorded in the form of the presence or absence of pits with a given depth and length. The pit information is reproduced with a read beam of a single wavelength.
The amount of information recordable on such an optical disk is restricted by the sizes of the pits and the read beam spot (the wavelength .lambda. and the number of apertures NA of the objective lens), so that the recording density has reached the maximum level at present.
It is therefore difficult to further improve the recording density of information on an optical disk.